Internal combustion engines of a motor vehicle are not able to initiate their active operation independently. For this reason, in conventional vehicles, the internal combustion engines are set in motion by an electrically operated starter. The necessary processes of mixture formation, combustion, engine-speed sensing and charge sensing of the internal combustion engine are started simultaneously with the operation of the starter. The independent running of the internal combustion engine is recognized when the speed of the internal combustion engine is above the speed of the starter or when the speed of the internal combustion engine exceeds a defined threshold. When the internal combustion engine has started to move independently, the starter is decoupled again from the internal combustion engine.
In hybrid systems which have two power plants in the form of the internal combustion engine and an electric motor, the internal combustion engine may be started by the electric motor or by the starter. With such a hybrid drive, it is possible to start the internal combustion engine from the motor-vehicle standstill. However, it is also possible to start the internal combustion engine during operation solely on electrical power with the electric motor as drive. The transition from electrical operation to hybrid operation, in which the electric motor or the starter starts the internal combustion engine and the vehicle is then powered by the electric motor and the internal combustion engine, may be initiated in the following manner. An interrupting clutch, situated between the internal combustion engine and the electric motor, is closed, and the electric motor tow-starts the internal combustion engine until the internal combustion engine is running on its own.
A further possibility is that the interrupting clutch between the internal combustion engine and the electric motor is initially open. While the vehicle is in operation, the interrupting clutch is then closed in a dragging fashion in the form of a proportional clutch or abruptly with the aid of an impulse clutch or a proportional clutch. In the cases described, it is not possible to say whether the internal combustion engine is running independently based on the analysis of the speed of the internal combustion engine, since the internal combustion engine may be pulled along by the electric motor.